VICS [Vehicle Information Communication System] comes to be used with spread of car navigation systems, and vehicles are provided with road traffic information, e.g., traffic jam information as VICS information. Road-o-vehicle communication and FM multiplex communication are carried out in order to provide the VICS information to the vehicles. In the case of the road-to-vehicle communication, an optical beacon is installed on a road and a vehicle is equipped with a receiving device compatible with the optical beacon. In the case of the optical beacon, each lane is provided with a head for transmitting and receiving data, and each head simultaneously downlinks the VICS information common to every lane, to each lane.
Furthermore, utilization of the optical beacon is under study to implement driving support by a vehicle infrastructure integration (VII) service. The VII service with the optical beacon is, for example, as follows: a vehicle performs position estimation based on reception of data from the optical beacon and calculates a distance from the vehicle to a stop line, based on the position estimation. Then the vehicle acquires signal light information and offers various types of driving support based on the distance information to the stop line and the signal light information. The signal light information is cycle information of signal lights of the respective colors and a right turn signal and the signal light information differs lane by lane, e.g., depending upon whether a lane is a straight through lane or a right turn lane. Therefore, for operating the VII service, it is necessary to set the information lane by lane, to make the optical beacon downlink different pieces of information for respective lanes from the corresponding heads, and to provide different services for the respective lanes.
However, a part of a downlink area of a head for each lane of the optical beacon lies in an adjacent lane. For this reason, when the heads transmit the different data for the respective lanes, interference of data occurs because of leakage from the adjacent lane, so as to cause a reception error, resulting in failure in receiving all necessary data. The communication device described in Patent Document 1 (Japanese Patent Application Laid-open No. 2000-182190) is configured to transmit the common data common to every lane, to all the lanes, and then to transmit lane-by-lane data to a selected one of the lanes while suspending the data transmission to a lane adjacent to the selected lane (i.e., perform transmission in time division between the lanes), thereby avoiding the interference of data between the lanes.